Human infection with the human immunodeficiency virus (HIV) and infection of rhesus monkeys with the closely-related simian immunodeficiency virus (SIV) often results in debilitating neuropathologic sequelae. In humans this is termed the AIDS dementia complex (ADC). While infection of rhesus macaques with SIV is considered a good animal for HIV infection and its neurologic sequelae neuronal loss characteristic of late stages of ADC has not been shown in SIV-infected macaques. Therefore, to determine whether neuronal loss/dysfunction occurs in the brain of macaques infected with SIV as previously demonstrated in HIV-infected patients, we quantified N-Acetyl Aspartate (NAA), a recognized neuronal marker, in extracts of SIV infected and control macaque brain by high resolution NMR. A histological analysis was also performed and the results correlated with NAA findings. We found significantly reduced NAA in the SIV group compared to controls (2.9+1.37; 6.2+1.73 mmols/g wet weight, respectively). A decrease in NAA was also found in the CNS tissues of SIV-infected animals sacrificed in the acute stages of infection. Trends were found between the NAA content and severity of histopathologic alterations.